This is true. Marvel stands to make more money by making a Black Panther/Captain Marvel/whoever film, making that character an A-lister and adding them to Avengers rather than splitting profits with Sony, and aren't they getting profit off that anyway?

Now what Marvel Studios *does* have, honestly, is the TV rights, and I believe that includes live action. They can include Spider-Man as a TV series so long as they don't involve/reference him in the movies. That would be interesting to see happen.

Disney also holds the complete merchandising rights to the Marvel films, which means they're making tons of risk free profit.